Method for softening cobalt alloy steel



Patented Nov. 21, 1933 UNITED STATES PATENT OFFICE Clifford A. Nickle, Schenectady, N. Y., assignor to General Electric Company,

New York a. corporation of No Drawing. Application June 29, 1931 Serial No. 547,789

Claims.

The present invention relates to cobalt steel and more particularly to cobalt steel of the type disclosed in Honda Patents No. 1,338,132; 1,338,- 133 and 1,338,134. Ordinarily, steel of this char- 5 act-er is extremely hard and brittle and practically unmachinable. Although it may be drilled by employing specially hardened tools such tools have to be resharpened frequently even when drilling relatively short holes. Heretofore, attempts have been made to soften cobalt steel by slowly cooling it from about 750 C. The prior process however has several disadvantages. It is long, usually causes impairment of the magnetic qualities of the steel, and does not always result in appreciable improvement of machinability.

The object of the present invention is to provide an inexpensive, reliable and relatively short process for softening cobalt alloy steel whereby the steel is made easily machinable and its magnetic properties are unimpaired.

The composition of the steel employed in my improved method may be similar to the composition disclosed in the above Honda patents.

" Such compositions may contain from about 5 to 60% cobalt, l to 10% tungsten, 0.5 to 10% chromium, 0.5 to 2% carbon and the remainder iron. Molybdenum may be substituted for the tungsten and if desired both the tungsten and molybdenum may be omitted. I prefer to employ a composition of the above character containing more than cobalt. The best results however have been obtained with a composition containing about 42% cobalt, 3% chromium, 2% tungsten, 0.5% manganese, 0.8% to 1.1% carbon with the remainder iron. I

In carrying out my invention the ingredients of the composition may be melted at a temperature varying from about 1600 to 1700 C. and then forged at about 1100 C. to 950 C., the forging operation being terminated at the latter temperature. The Wrought material is then air cooled to room temperature. The wrought alloy is very hard and practically unmachinable at this time. To soften the alloy I heat it to about 825 C. and quickly cool either by quenching in oil or by air cooling. The alloy is now relatively soft and easily machinable. After any machine work on the alloy is completed it is hardened by reheating to about 930 C. and quenching in oil. It is then magnetized.

If there is uncertainty as to whether or not the forging operation was terminated at about 950 C., the forged material should be reheated to about 930 to 950 C. and then quickly cooled.

Thereafter it may be softened as heretofore indicated by heating to about 825 C. and quickly cooling in air or quenching in oil. The alloy may then be machined as desired and thereafter hardened by reheating to 930 C. and quenching in oil. The hardened material may then be magnetized.

If the piece to be treated is of cast instead of wrought material the above procedure may be varied slightly. In making a cast magnet the ingredients of the alloy are melted at a temperature of about 1600 to 1700 C. and then cast in a mold. The casting is then normalized by heating at a temperature of about 1100 C. for an appreciable period of time which will of course vary with the size of the casting. As an example, a casting about 3" thick would require a. heating period of about 6 hours duration. After the casting is normalized it is air cooled to a temperature well below 850 C. for example to about 550 C. at which temperature it will be in a black condition. The casting is then reheated to 930 to 950 C., rapidly cooled by oil quenching or air cooling, reheated to about 825 C. and again rapidly cooled by oil quenching or air cooling. The casting may then be machined as desired, thereafter hardened at a temperature of about 950 C., quenched in oil and magnetized.

The temperature at which the casting or wrought materials are heated in order to effect softening thereof is somewhat critical. While I prefer to employ a temperature of about 825 C. thls temperature may be varied about 25 either way. Cobalt alloy steel softened in accordance with my process may be machined easily and when thereafter hardened and magnetized the magnetic properties of the steel are equal to the magnetic properties of cobalt alloy steel which has not been subjected to a softening treatment.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of softening cobalt alloy steel to render it easily machinable which comprises heating the steel to a temperature of about 800 C. to about 850 C. and quickly cooling.

2. The method of softening cobalt alloy steel to render it easily machinable which comprises heating the steel to a temperature of about 825 C. and quickly cooling.

3. The method of treating cobalt alloy steel 105 to render it machinable which comprises heating the steel at about 930 C. to about 950 C., quickly cooling, reheating at about 800 C. to 850 C. and quickly cooling.

4. The method of preparing permanent mag- 9 the ingredients comprising said magnet to form an alloy, casting the molten material in a mold, normalizing the casting at a temperature of about 1100 0., heating the casting at 930 to 950 C., quickly cooling it, reheating to 800 to 850" C., quickly cooling the casting, machining it, herdening the casting by heating it to 930- C. to 13-30 C., quickly cooling and'thereaiter magnetizing it.

CLIFFORD A. NICKLE. 

